1. Technical Field
The present invention relates generally to cable assemblies. More particularly, the present invention relates to a cable assembly whose condition is monitorable so that the cable assembly may be replaced prior to the failure of one or more critical conductors. The present invention also relates to a system and method for monitoring the condition of a cable assembly.
2. Discussion
Cable assemblies are commonly employed in industrial and telecommunications operations to transmit electrical power and/or signals between two devices. In situations where the two devices operate in stationary positions and are not exposed to environmental agents such as sunlight or chemicals that cause their insulating covers to degrade, the cable assembly will last indefinitely. However, where one device moves relative to the other, the cable assembly is susceptible to fatigue failures wherein one or more of the conductors that make up the cable assembly break due to repeated bending. Similarly, where the cable assembly is exposed to environmental agents which degrade the cable assembly""s insulating material, the insulating material can fail causing the conductors that make up the cable assembly to come into electrical contact with one another or with an electrical ground.
Failures of these types are often catastrophic, completely disabling the devices to which they are coupled. Complicating matters is that these types of failures are typically difficult to predict and rather time consuming to repair. Repair may consist of the wholesale replacement of the cable assembly, or it may comprise the removal and replacement of one or more areas that are suspected of being damaged.
To combat down-time associated with failures in cable assemblies, some users of cable assemblies simply incorporate additional (spare) conductors into the cable assembly which are then be used to replace one of the actively used conductors upon the occurrence of a fault. This solution, however, has several drawbacks. One drawback relates to fact that the additional cables can be relatively expensive and as such, the incorporation of spare cables further increase the cost of the cable assembly. Another drawback relates to the ease with which the additional cables are festooned between the devices and the impact of additional cable weight on the person or mechanism that must position the device or devices that are coupled to the cable assembly. Yet another drawback concerns the occurrence of a failure related down-time. Failures in an active conductor will still result in some down-time, albeit a smaller amount of down-time than had the cable assembly not included a spare.
Another approach has been to predict a lifespan of the cable assembly and simply replace the cable assembly after it has been in use for a duration equal its lifespan, regardless of its actual condition. This approach, however, has not been completely successful due difficulties in calculating the lifespan of the cable assembly. Furthermore, this approach is rather costly, as cable assemblies are replaced regardless of their actual condition.
It is one object of the present invention to provide a cable assembly which may be readily monitored so that its condition can be determined prior to the failure of a conductor which is necessary for the operation of the devices to which the cable assembly is connected.
It is another object of the present invention to provide a cable assembly having a sacrificial conductor which permits the condition of the cable assembly to be monitored.
It is a further object of the present invention to provide a cable condition monitoring system for generating an alarm signal in response to the detection of a fault in a sacrificial conductors in the cable assembly.
It is yet another object of the present invention to provide a method for monitoring the condition of a cable assembly.
In one preferred form, the present invention provides a cable assembly having a critical conductor and a sacrificial conductor. The critical conductor has a fatigue life of a predetermined first length and the sacrificial conductor has a fatigue life of a predetermined second length which is shorter than the predetermined first length such that exposure of the cable assembly to repeated flexure causes the sacrificial conductor to fail before the critical conductor fails. A cable condition monitoring system for generating an alarm signal in response to the detection of a fault in the sacrificial conductors and a method for monitoring the condition of a cable assembly are also provided.